Distinguish EOF and () in read()

2 files changed, 7 insertions, 2 deletions

diff --git a/actinide/reader.py b/actinide/reader.py
index 0955309..f7703b5 100644
--- a/actinide/reader.py
+++ b/actinide/reader.py
@@ -10,6 +10,10 @@ from .types import *
 class SyntaxError(Exception):
     pass
 
+# Returned on ``read`` if it has reached the end of the input. This is a
+# special, non-interned token guaranteed to be unequal to any other token.
+EOF = Symbol('#<end-of-input>')
+
 # Reads one form from a port. This will consume all of the tokens included in
 # the form, but leave trailing data after the final token untouched.
 #
@@ -23,7 +27,7 @@ class SyntaxError(Exception):
 def read(port, symbols):
     head = read_token(port)
     if head is None:
-        return None
+        return EOF
     if head == ')':
         raise SyntaxError("Unexpected ')'")
     if head == '(':
diff --git a/bin/actinide-repl b/bin/actinide-repl
index de19617..c4343b6 100755
--- a/bin/actinide-repl
+++ b/bin/actinide-repl
@@ -3,6 +3,7 @@
 import sys
 
 import actinide as a
+import actinide.reader as ar
 import actinide.ports as ap
 import actinide.types as at
 
@@ -12,7 +13,7 @@ def repl(session, port):
             sys.stdout.write("> ")
             sys.stdout.flush()
             form = session.read(port)
-            if form is None:
+            if form is ar.EOF:
                 print()
                 return 0
             results = session.eval(form)